Conference Agenda

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The objective of this CLIMATE-TPE project is: To improve the understanding of the interactions between the Asian monsoon, the plateau surface (including its permafrost and lakes) and the Tibetan plateau atmosphere in terms of water and energy budgets in order to assess and understand the causes of changes in cryosphere and hydrosphere in relation to changes of plateau atmosphere in the Asian monsoon system and to predict the possible changes in water resources in the Third Pole Environment. A core innovation of the project is to verify or falsify recent hypotheses (e.g. links between plateau heating and monsoon circulation, snow cover and monsoon strength, soil moisture and timing of monsoon) and projections of the changes of glaciers and permafrost in relation to surface and tropospheric heatings on the Tibetan plateau as precursors of monsoon pattern changes and glaciers retreat, and their impacts on water resources in South East Asia.

We use earth observation, in-situ measurements and modelling to advance process understanding relevant to monsoon scale predictions, and improve and develop coupled regional scale hydroclimatic models to explain different physical links and scenarios that cannot be observed directly. Three work-packages (WP) are defined in the project to address three specific objectives. Objective 1) advancement of the understanding of microwave scattering and emission under complex terrains with permafrost and freeze – thawing conditions. The focus is to reduce current uncertainties in microwave satellite observations over complex terrain and improve retrieval accuracies of soil moisture and freeze-thaw states by deploying in-situ observations, laboratory experiment and numerical modelling. Objective 2) Advancement of physical understanding and quantification of changes of water and energy budgets in the TPE. The focus here is to integrate current understandings in the mechanism of changes in water and energy budget in TPE using satellite data products and numerical modelling. Objective 3) Advancement of quantifying changes in surface characteristics and monsoon interactions. All variables related to water and energy budgets in TPE will be subject to systematic analysis to endure their consistence in terms of climate data records. The variables will include albedo, vegetation coverage, soil thermal and hydraulic properties, LST, soil moisture, lake levels and land use changes among others.

In this contribution we focus on WP1: Observation and modelling of microwave scattering and emission under complex terrains and including permafrost and freeze and thawing.

We have deployed the ESA L-band (1.41 GHz) Radiometer (ELBARA-III, Schwank et al. 2010) since the beginning of 2016 at the central micrometeorological station (latitude: 33.919750, longitude: 102.153183, WGS’84) of the Maqu network of the Tibetan Plateau. ELBARA-III is provided by ESA for experimental observation for the calibration and validation of SMOS data and products.

1) We have conducted ELBARA measurements, covering one complete freeze-thawing cycles, for advancing understanding of the mass and energy exchanges involved in the freeze/thaw process.

2) The collected ELBARA observations are analysed with the recently developed effective temperature model by Lv et al. (2014) to better understand the microwave emission signals, including the validation of ESA’s SMOS and NASA’s SMAP radiometer brightness temperatures (TB).

3) The collected ELBARA and other in-situ data are used to investigate the effectiveness in two recently developed methods to merge existing satellite data of different frequencies (e.g. for low resolution data SCAT/ASCAT, SSM/I, AMSRE-E/2, SMOS, and high resolution data ASAR/S-1) (Dente et al. 2014; Lv et al. 2014), so that a consistent soil moisture data product can be generated by using the same consistent framework, contributing to the ESA Climate Change Initiative.

The Third Pole Environment (TPE) centered on the Tibetan plateau and the Himalayas feeds Asia s largest rivers which provide water to 1.5 billion people across ten countries. Due to its high elevation, TPE plays a significant role in global atmospheric circulation and is highly sensitive to climate change. Intensive exchanges of water and energy fluxes take place between the Asian monsoon, the plateau land surface (lakes, glaciers, snow and permafrost) and the plateau atmosphere at various temporal and spatial scales, but a fundamental understanding of the details of the coupling is lacking especially at the climate scale. Based on in-situ measurements, satellite remote sensing and numerical modeling, several main achievements have been acquired to promote the understanding of water and energy cycles over the Tibetan Plateau. (1) In-situ measurements: Systematic underestimations of soil heat flux by soil heat flux plate have been proved with estimation from in-situ soil moisture and temperature measurements in CAMP/Tibet. The comparison between in-situ soil heat flux and estimated values from temperature prediction-correction method shows that they have the same heat flux flow direction and phase. However, the in-situ values measured by heat flux plate are generally smaller than the estimation. It was also identified that variations in soil moisture had important effects on carbon exchange in this alpine steppe ecosystem. Both the photosynthesis and respiration were active under high soil moisture content, and suppressed during periods of water shortage. Precise measurements of evaporation and understanding of the physical controls on turbulent heat flux over lakes at different time scales have fundamental significance for catchment-scale water balance analysis and local-scale climate modeling. To test the performance of lake-air turbulent exchange models over high-altitude lakes and to understanding the driving forces for turbulent heat flux and obtain the actual evaporation over the small high-altitude lakes, an eddy covariance observational system was built above the water surface of the small Nam Co Lake. Also we analyzed the variability and trends of daily precipitation extremes over the northern and southern side of central Himalaya, case study on evaluation of future precipitation scenario using statistical downscaling model over humid, sub humid and arid region of Nepal. (2) Remote sensing: Combing satellite remote sensing data and surface meteorological forcing data, land surface heat fluxes at multi-spatiotemporal scales over the Tibetan Plateau have been achieved. The parameterization schemes for diffused and reflected downward shortwave radiation flux of the TESEBS model were improved by introducing the parameters sky-view factor (SVF) and terrain configuration factor (Ct). (3) Model simulation: WRF model was used to estimate surface parameters and related meteorological elements over the Tibetan Plateau. The ground-measured surface variables and land surface heat fluxes were compared to WRF model values. The comparisons show good consistency. Lake-air interactions at Nam Co lake were analyzed through evaluating two popular lake-air exchange models: a bulk aerodynamic transfer model (B Model) and a multi-layer model (M Model). It was found that both models underestimated turbulent fluxes. This was due to inaccurate values of the Charnock coefficient and the roughness Reynolds number which are both important parameters for calculating the roughness length for momentum over water. Also Regional Atmospheric Modeling System (RAMS) was applied to the study of the effect of the topographical altitude of the Tibetan Plateau (TP) on a severe drought event which took place in eastern China from November 2008 to January 2009. (4) Hydrological model: Flow generated from Upper Indus Basin (UIB) originates in Hindukush-Karakoram-Himalaya region, Pakistan. The initial water supply reinstates after winter, depending upon the accumulated snow aggregate and subsequent temperature. Seasonal temperature dictates the state and fate of snow and glacier melt during summer. Recently, developing evidence of warming at high-mountains is accelerated regarded as Elevation dependent warming (EDW). We have identified trends, analyzed variability, and assessed changes in annual and seasonal maximum, minimum, mean and diurnal temperature range. (5) Training of young scientists in the area of climate and environment. Four PhD students have been sent to European partner for joint training. Two of them have got PhD degree in University of Twente under the supervision of European PI (Prof. Z. (Bob) Su) and Chinese PI (Prof. Yaoming Ma). Several European students from our partner also come to China regularly for joint field visiting and academic exchange.

Surface soil moisture (SSM) plays a significant role in various domains of science such as agriculture, hydrology, meteorology and ecology. However, the spatial resolution of microwave SSM products is too coarse for regional and local applications. Most of the current optical/thermal infrared SSM retrieval models cannot estimate the quantitative volumetric soil water content directly without establishing empirical relationships between SSM measurements and satellite derived proxies of SSM. Therefore, this study mainly estimates SSM directly from Chinese geostationary meteorological satellite FY-2E data with a high spatial resolution of 5 km based on an improved elliptical SSM retrieval model developed from the synergistic use of the diurnal cycles of Land Surface Temperature (LST) and Net Surface Shortwave Radiation (NSSR). The original model is developed with bare soil. The coefficients of the original model are not distinguished from different Fractional Vegetation Cover (FVC). To optimize the model for SSM estimation at regional scale, the present study improved the original model by accounting for the influence of FVC, which is based on a dimidiate pixel model and MODIS NDVI product. Ultimately, a preliminary validation was conducted using the ground measurements in the south of Maqu City, in the source area of the Yellow River. A correlation coefficient (R) of 0.620, a root mean square error (RMSE) of 0.146 m3/m3 and a bias of 0.038 m3/m3 are found between in-situ measurement and FY-2E-derived SSM from original model. While it reveals a better relationship between FY-2E-derived SSM from improved model and ground measurement with a R of 0.845, a RMSE of 0.064 m3/m3 and a bias of 0.017 m3/m3. In order to provide more accurate SSM, high accuracy FVC, LST and NSSR are still needed. In addition to the point scale validation, cross comparison with other existing SSM products will be conducted in the future studies.

Poster

Monitoring sensible heat flux over urban areas in a high-altitude city using Large Aperture Scintillometer and Eddy Covariance

Urbanization leads to modifications of surface energy balance which governs the momentum, heat and mass transfer between urban canopy layer and the atmosphere, thus impacts dynamic processes in the urban ABL and ultimately influence the local, regional and even global climate. It is essential to obtain accurate urban ABL observations to enhance our understanding of land-atmosphere interaction process over the urban area and help to improve the prediction ability of numerical model. However, up to now, there are rarely observations in high-altitude cities. This poster introduced the urban flux observation conducted in a high-altitude city, Lhasa, using eddy-covariance technique and large aperture Scintillometer. As the first results, the diurnal patterns of the surface energy balance and energy partitioning in the winter of 2016 were discussed.

Poster

Evaporation and energy budget observation over a high-altitude small lake on the Tibetan Plateau

Lakes are an important part of the landscape on the Tibetan Plateau. The area that contains most of the plateau lakes has been expanding in recent years, but the impact of lakes on lake-atmosphere energy and water interactions is poorly understood and precise measurements of evaporation and understanding of the physical controls on turbulent heat flux over lakes at different time scales is rarely studied due to lack of observational data. To meet the above demands, an eddy covariance observational system was built above the water surface of the small Nam Co Lake (with an altitude of 4715 m and an area of approximately 1.4 km2, mean depth of 7 m) in April 2012 and the results are given by using data over ice free periods in 2012 and 2013 as follows: Firstly, the roughness length for momentum is 3.35×10-4 m over the small lake and the atmosphere is dominated by unstable and neutral conditions. The proper Charnock coefficient (α=0.031) and the roughness Reynolds number (R_r=0.56) for z_0m simulation are obtained for Bulk aerodynamic transfer model (B model) simulation. The simulated heat flux is validated independently with observations in 2013. The B model, with parameters optimized for the specific wave pattern in the small lake, could provide reliable and consistent results with EC measurements, and B model simulations are suitable for data interpolation due to inadequate footprint or malfunction of the EC instrument. Secondly, wind speed shows significance at half-hourly time scales, whereas water vapor and temperature gradients have higher correlations over daily and monthly time scales in lake-air turbulent heat exchange. Lastly, the total evaporation in this small lake (approximately 812 mm) is approximately 200 mm larger than that from adjacent Nam Co (approximately 627 mm) during their ice-free seasons. Moreover, the energy stored during April to June is mainly released during September to November, suggesting an energy balance closure value of 0.97 over the entire ice-free season. These results provide a foundation for application of remote sensing data over the high-altitude small lakes.